The present applicant has proposed an imaging device which has an electronic shutter function to adjust the exposure time without using a mechanical iris, by controlling the effective charge storage time of an interline transfer (IT) type solid-state imaging element (CCD image sensor), in the U.S. Pat. No. 5,157,502.
In this imaging device, electric charges stored in each pixel of a photoelectric converter of the CCD image sensor are read out to a vertical transfer section by a sensor gate signal SG shown in FIG. 1B which is outputted in a vertical interval time code VBLK during which a vertical interval signal VB shown in FIG. 1A falls to a low level. The charge storage time of the CCD image sensor is controlled by a reset signal RT shown in FIG. 1C. When this reset signal RT is supplied to the CCD image sensor, it sweeps the electric charges stored in the pixels to an overflow drain.
Therefore, in a period (charge sweep period TI) during which the reset signal RT is supplied every one horizontal period (1H), the effective charges are not stored in the CCD image sensor. Thus, the effective charges are stored in the photoelectric converter of the CCD image sensor from when the reset signal RT supplied to the CCD image sensor is stopped. By controlling the timing to stop the reset signal RT, the effective charge storage time TE, that is, the shutter speed, may be controlled.
In the above-described imaging device, the shutter speed may be varied in response to the movement of an object by using such electronic shutter function. Therefore, the imaging device is advantageous particularly for intake of an image with respect to a high-speed moving object.
As an imaging device for factory automation (FA), for example, an imaging device having a structure as shown in FIG. 2 for imaging a moving object is known. In this imaging device, when an object 2 moving on a moving path 1 moves toward an imaging section 3, an object detector 4 detects the object 2 and supplies a trigger signal TRIG which falls to a low level at a timing t11 shown in FIG. 3A to a shutter signal generating circuit 5 and a synchronizing signal generating circuit 8.
When the trigger signal TRIG is supplied to the shutter signal generating circuit 5, it supplies a shutter control signal STC which rises at the fall timing t11 of the trigger signal TRIG, as shown in FIG. 3B, to a CCD control circuit 6.
The CCD control circuit 6 supplies a reset signal RT for sweeping electric charges stored in a photoelectric converter of the CCD image sensor 7. When the trigger signal TRIG is supplied, the CCD control circuit 6 stops supplying the reset signal RT to the CCD image sensor 7. Thus, storage of effective charges into each pixel of the photoelectric converter of the CCD image sensor 7 is started.
The CCD control circuit 6 is supplied with a vertical synchronizing signal VD which is at a low level during the period from the timing t11 to a timing 12, as shown in FIG. 3C, and a horizontal synchronizing signal HD from the synchronizing signal generating circuit 8. When the shutter control signal STC is supplied to the CCD control circuit 6, it counts nine pulses of horizontal synchronizing signal HD shown in FIG. 3D from the fall timing t11 of the vertical synchronizing signal VD shown in FIG. 3C. After that, the CCD control circuit 6 counts a predetermined number of master clocks, and then supplies a sensor gate signal SG which rises at a timing t13 shown in FIG. 3E to the CCD image sensor 7.
Thus, during the period from when the shutter control signal STC rising at the timing t11 shown in FIG. 3B is supplied to the CCD image sensor 7 until the sensor gate signal SG rising at the timing t13 shown in FIG. 3E is supplied to the CCD image sensor 7, electric charges corresponding to an imaging light radiated through an imaging lens 9 are stored in the CCD image sensor 7. The period from the timing t11 to the timing t13 becomes an effective charge storage time TE.
FIG. 3F shows a vertical interval time code VBLK.
The electric charges read out from the CCD image sensor 7 are supplied as an imaging signal to a signal processing circuit 10. The signal processing circuit 10 performs signal processing, such as, appending a synchronizing signal to the imaging signal, and outputs the processed signal as a video signal through an output terminal 11. The video signal outputted through the output terminal 11 is supplied to, for example, a monitor. Thus, the state of the object 2 in the case where the object 2 is moved may be analyzed.
In this manner, in this imaging device, the vertical synchronizing signal VD is generated and storage of effective charges is started in response to the trigger signal TRIG supplied from the object detector 4, thereby imaging the moving object 2.
Meanwhile, since the imaging device for imaging a moving object is used mainly for FA, there is a case where it is intended to move the object 2 shown in FIG. 2 at a high speed so as to carry out imaging by a high-speed shutter of 1/10000 seconds, for example.
In the above-described imaging device, however, the output timing of the sensor gate signal SG is preset and fixed on the basis of the pixel array of the CCD image sensor. For example, the sensor gate signal SG is supplied to the CCD image sensor at the timing when a predetermined number of clocks are counted after nine pulses of the horizontal synchronizing signal HD are counted from the fall of the vertical synchronizing signal VD. Therefore, in the imaging device which performs imaging operation by generating the vertical synchronizing signal VD from the trigger signal TRIG, the effective charge storage time cannot be reduced to not longer than the time period from the fall timing of the vertical synchronizing signal VD to the output timing of the sensor gate signal SG. Accordingly, it has been difficult to carry out imaging by a high-speed shutter of 1/10000 seconds.
On the other hand, there is another case where it is intended to carry out image processing of a video signal from the imaging device by using an image processing equipment. In general, the image processing equipment operates with reference to a predetermined synchronizing signal. Therefore, in the case where video signals from plural imaging devices and video recording/reproducing devices are to be compounded, video signals synchronized with a synchronizing signal as a reference need to be supplied to the image processing equipment.
In the imaging device in such case, if a trigger signal TRIG is supplied at an arbitrary timing as shown in FIG. 4A, after a predetermined effective charge storage time, that is, after a predetermined exposure time, a sensor gate signal SG shown in FIG. 4B is supplied to the CCD image sensor and electric charges stored in each pixel of the photoelectric converter are read out to the vertical transfer section. At the same time, a vertical synchronizing signal V-SYNC is generated so that the electric charges read out to the vertical transfer section are outputted as an imaging signal VIDEO through a horizontal transfer section in synchronization with the generated vertical synchronizing signal V-SYNC, as shown in FIG. 4C. In this imaging device, the video signal VIDEO is outputted at a random interval as shown in FIG. 5B in response to the trigger signal TRIG supplied at an arbitrary timing, that is, randomly, as shown in FIG. 5A. Therefore, the vertical synchronizing signal V-SYNC cannot be outputted in a constant cycle.
Alternatively, in this imaging device, a vertical synchronizing signal V-SYNC of a constant cycle is generated as shown in FIG. 6C. If a trigger signal TRIG shown in FIG. 6A is supplied, after a predetermined exposure time, a sensor gate signal SG shown in FIG. 6B is supplied to the CCD image sensor and electric charges stored in each pixel of the photoelectric converter are read out to the vertical transfer section. At the same time, the vertical synchronizing signal V-SYNC is generated at the timing based on the trigger signal TRIG, unlike the previously generated vertical synchronizing signal V-SYNC.
Meanwhile, with respect to video processing equipments, such as, a frame memory and a monitor, for processing video signals from the imaging device as described above, the operation must be synchronized with the supplied video signals.
However, in these video processing equipments, synchronization with the synchronizing signal of a random cycle is technically very difficult and therefore is not carried out generally.
Thus, it is an object of the present invention to provide a driving control method for an imaging element, an imaging device, an imaging control device and an imaging system which enable performing imaging operation by a high-speed random shutter synchronized with the trigger signal and obtaining effective charges in a predetermined imaging range as an imaging signal.
It is another object of the present invention to provide a driving control method for an imaging element, an imaging device, an imaging control device and an imaging system which enable obtaining an imaging signal in an arbitrary image range.
Also, in such sports fields as track race and swimming race where the speed is important, the goal decision is made with a precision of 1/100 seconds.
Thus, it is still another object of the present invention to provide an imaging control method, an imaging control device, an imaging system and an imaging device which enable composition of images having a time difference of 1/100 seconds into one image and output of the composite image.
It is a further object of the present invention to provide an imaging control method, an imaging control device, an imaging system and imaging device which enable imaging of a fast moving object with a predetermined time difference, composition of images into one image, and output thereof.